Collaborative Research: Genetic diversity, resistance genes, and negative density dependence in tropical tree seedling dynamics

热带森林以其高度的多样性以及大量的稀有物种而闻名。最近的研究发现，与普通物种相比，稀有的热带树种更容易受到病原体的侵害，这些病原体专门针对单一宿主物种，然后通过该单一宿主的密集幼苗迅速传播。这项研究将验证一种新的假设，即稀有物种受到宿主特异性病原体的影响更大，因为它们在种群水平上具有较低的抗性基因多样性，因此它们所有的幼苗都对同一组病原体敏感，从而促进病原体的快速传播并增加死亡率。这一假设将通过温室实验和实地研究进行检验，并结合遗传分析，量化巴拿马巴罗科罗拉多岛低地热带森林中稀有和常见树种的抗性基因多样性。计算机模拟还将被用来检查抗性基因多样性的测量差异是否会影响感染水平、死亡率和当地树种的丰度。这项研究的结果将提高对植物与病原体相互作用的认识，并在农业和园艺方面具有潜在的应用价值（例如提高作物的病原体抗性）。通过为学生和教师举办的夏季讲习班，将向更广泛的受众提供尖端遗传技术的实践培训。这项研究将首次从树木群落中获得大型转录组数据集，并将提供基因序列数据，为未来热带森林遗传多样性的研究提供信息。对抗性基因多样性对森林动态的影响的研究将弥合分子进化研究之间的差距，这些研究表明在许多位点上多种抗性基因正在进行选择，以及这种多样性如何在自然界中发挥作用。此外，这项研究可能通过提供遗传解释来解释为什么稀有树种更容易受到其特定物种敌人的强烈控制，从而连接有关热带植物多样性的竞争理论，同时支持扩散限制作为决定哪些物种在当地占主导地位的特征。最终，这项研究应该阐明，局部稀有是否限制了局部遗传多样性，而遗传多样性反过来又强化了局部稀有，这种循环只能通过远距离花粉或种子运动吸收新的等位基因来避免。证明种群的生态特征和遗传特征之间的这种耦合将为进化和生态学的理论进步带来新的视角和途径。该项目将为本科生和研究生以及博士后研究员提供研究经验。

Tropical forests are famous for their high diversity, as well as the large number of rare species they harbor. Recent studies have found that, compared to common species, rare tropical tree species suffer more from pathogens that are specialized to a single host species that then spread rapidly through dense patches of seedlings of that single host. This research will test the novel hypothesis that rare species are more strongly impacted by host-specific pathogens because they have lower diversity of resistance genes at the population level, such that all their seedlings will be susceptible to the same suite of pathogens, promoting rapid pathogen spread and increasing mortality rates. This hypothesis will be tested using experimental greenhouse and field studies, combined with genetic analyses that will quantify the diversity of resistance genes for rare and common tree species in lowland tropical forest on Barro Colorado Island, Panama. Computer simulations will also be used to examine whether the measured differences in resistance gene diversity would impact infection levels, mortality rates and local abundance of tree species. Results of this study will improve understanding of plant-pathogen interactions, with potential applications for agriculture and horticulture (e.g. increasing pathogen resistance in crops). Hands-on training in cutting-edge genetic techniques would be provided to a wider audience through a summer workshop for students and faculty.This study will be the first to obtain large transcriptome datasets from a tree community and will provide gene sequence data that will be informative for future studies of genetic diversity in tropical forests. Examination of the effects of resistance gene diversity on forest dynamics will bridge the gap between molecular evolution studies that indicate ongoing selection for multiple resistance genes at many loci, and how this diversity functions in nature. Furthermore, this study is likely to bridge competing theories for tropical plant diversity by providing a genetic explanation for why rare tree species are more strongly controlled by their species-specific enemies, while simultaneously supporting dispersal limitation as a feature determining which species are locally dominant. Ultimately, the study should elucidate whether local rarity restricts local genetic diversity, which in turn reinforces local rarity, a cycle that can be escaped only by recruitment of new alleles via long-distance pollen or seed movement. Demonstrating such a coupling between the ecological and genetic features of populations would bring new perspectives and avenues for theoretical advances in evolution and ecology. The project will provide research experiences for undergraduate and graduate students, as well as a postdoctoral researcher.